This invention relates to additives for polyphenylether lubricants.
Tricresyl phosphate (TCP) is a widely used and effective antiwear additive for a variety of lubricants used in aerospace applications. However, for high-temperature gas turbine engine oil (GTO) applications, volatility and thermo-oxidative stability limitations preclude the use of TCP.
Gas turbine engine oil requirements for the next generation military engines are for high-temperature, i.e., 315.degree. to 370.degree. C., lubricants. One group of materials which satisfies this requirement is the aromatic ethers, i.e., C.sub.6 H.sub.5 --O--(--C.sub.6 H.sub.4 --O--).sub.n --C.sub.6 H.sub.5, where n is 2 to 4, or greater. For example, the base stock for MIL-L-87100, a 300.degree. C. GTO, is currently m-bis-(m-phenoxyphenyl) benzene. Other suitable base fluids are the thioaromatic ethers, cyclic phosphazines, and the like.
Efforts are underway to increase the upper use temperature of GTO lubricants either by modifying their chemical structure or by developing antioxidants capable of increasing the upper use temperature. Together with the need for higher temperature antioxidants, there is a need for an antiwear additive which is stable and effective at the higher temperature.
TCP has been found to be a good lubricity additive for the above-described base stock at 75.degree. C. with 52-100 steel and at 204.degree. C. with M50 steel. TCP is not, however, suitable for use at 315.degree. C. because its upper use temperature is about 290.degree. C.
Accordingly, it is an object of the present invention to provide a lubricity additive for GTO lubricants which is stable and effective at higher temperatures.
Other objects and advantages of the invention will be apparent to those skilled in the art.